1. Field of the Invention
This invention relates to an invertor-controlled power unit, and more particularly to an invertor-controlled power unit which is adapted to perform parallel operation together with other power units connected therewith.
2. Prior Art
In starting parallel operation of a plurality of invertor-controlled power units connected in parallel with each other, there are a case where an invertor-controlled power unit in stoppage have output lines thereof connected to output lines of an invertor-controlled power unit which has already been started to generate electricity, and then the power unit in stoppage is started for parallel operation, and a case where a plurality of invertor-controlled power units are first started to generate electricity and then have output lines thereof directly connected in parallel with each other to start parallel operation of the power units.
In both cases, a phase difference between waveforms of output voltages from the invertor-controlled power units in parallel operation causes electric current to alternately flow from one power unit to another due to a difference in output voltage between the power units, which may destroy component parts of the power units. Therefore, it is necessary to synchronize the phases of the output voltages from the power units with each other.
To this end, even in the case of parallel operation of identically-constructed invertor-controlled power units, it is required to provide wiring for transmitting signals for informing each other of operating conditions thereof. Further, as disclosed e.g. in Japanese Patent Publication (Kokoku) No. 56-20782, it is required to employ an automatic synchronizing device, and means for producing an operating point at which the phases coincide with each other, to thereby cause the automatic synchronizing device to reliably operate at early timing. Further, as disclosed in Japanese Provisional Utility Model Publication (Kokai) No. 62-145440, a special adaptor is used for parallel operation of two power units, with one of them serving as a master generator while the other serves as a slave generator.